I actually saw a similar large bolide over Poland last Sunday, also while travelling in a car. I think being in cars is what causes them, or something.
It's a crazy feeling when the immutable, dependable sky lights up like that all of a sudden - it's as if nature was waggling a finger at you, telling you it can kill you and everyone you love at any damn time it pleases, so you better keep some perspective on your life pretty please. :D